Cameron County, TX Accessory Structures: ADU Rules (2026)

Article 5, Section L of the county's Flood Damage Prevention and Building Regulations governs accessory dwelling units on unincorporated land. No ADU can be constructed, used or occupied until an accessory dwelling permit is issued, and only one ADU is allowed per lot, limited to lots where the principal use is a single-family detached dwelling.

Owner-occupancy is mandatory: the property owner, whether title holder or contract purchaser, must occupy either the main house or the ADU as a permanent residence and can never collect rent on the unit they occupy, proven by voter registration, vehicle registration or similar records and sworn in a notarized affidavit. The applicant must also record a covenant with the County recorder putting future buyers on notice that the ADU's legal existence depends on that owner-occupancy, and requiring removal of the ADU improvements if the condition is ever violated.

Size depends on lot area. On lots smaller than 10,000 square feet, the ADU cannot exceed 50 percent of the principal dwelling's square footage or 1,000 square feet, whichever is less. On lots of 10,000 square feet or larger, only the 50-percent cap applies. A detached ADU needs a minimum 5-foot setback from the rear and side property lines, must have its own exterior entrance with its own cooking, sleeping and sanitary facilities, and normally has to tie into the principal structure's central electrical, water and sewer service unless it sits more than 100 feet away.